Performance of a slow positron beam using a hybrid lens design

The University of Hong Kong positron beam employs conventional magnetic field transport to the target, but has a special hybrid lens design around the positron moderator that allows the beam to be focused to millimeter spot sizes at the target. The good focusing capabilities of the beam are made possible by extracting work-function positrons from the moderator in a magnetic field free region using a conventional Soa lens thus minimizing beam canonical angular momentum. An Einzel lens is used to focus the positrons into the magnetic funnel at the end of transportation magnetic field while at the same time bringing up the beam energy to the intermediate value of 7.5 keV. The beam is E × B filtered at this intermediate energy. The final beam energy is obtained by floating the Soa-Einzel system, E × B filter and flight tube, and accelerating the positrons just before the target. External beam steering saddle coils fine tune the position, and the magnetic field around the target chamber is adjusted so as to keep one of the beam foci always on the target. The system is fully computer controlled. Variable energy-Doppler broadened annihilation radiation (VEDBAR) data for a GaN sample are shown which demonstrate the performance of the positron beam system.     

Synthesis of 1,3,4‐Oxadiazole‐Based Aromatic and Heterocyclic/Phenylpyrazole Derivatives

A new series of 1,3,4‐oxadiazole‐based aromatic and heterocyclic/phenylpyrazole derivatives 6a–c , 7a–d , and 8 were synthesized via sequential 1,3‐dipolar cyclization, hydrazidation, benzoylation, dehydrative cyclization, and the Suzuki coupling reaction. Among the derivatives, compounds 7a and 7c with the corresponding 2‐thienyl and 2‐benzo[b]thienyl (Ar) at the phenyl group located at the N‐1 position of pyrazole showed a better conjugation range.      

Synthesis and biological evaluation of glycosylated psoralen derivatives

A novel route for the efficient synthesis of a target psoralen moiety, 4,4′-dimethylxanthotoxol, has been developed, which need only four steps using cheap pyrogallol as a starting material. Subsequently, a range of new glycosylated psoralen derivatives were synthesized in good yields with simple procedures and mild reaction conditions. The experiment of biological activity shows that some of the glycosylated psoralen derivatives have antiproliferative activities against human cancer cell lines. A strong photo-induced antiproliferative effects were found under UVA. All of the glycosylated psoralen derivatives exhibited antioxidant activities against the oxidation of DNA induced by Cu²⁺/glutathione (GSH). Further experiment also demonstrates that the introduction of sugar moieties in some glycosylated psoralen derivatives can improve their antioxidant activities significantly.     

Experimental verification of strong rotational dependence of fluorescence and predissociation yield in the b1Πu(v = 1) level of 14N2

New, rotationally resolved fluorescence-excitation spectra confirm coupled-channel Schro?dinger-equation predictions of strong rotational dependence of the fluorescence and predissociation yields in the b(v = 1) level of (14)N(2).     

Synthesis of 4‐(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)phenyl‐hydrazine derivatives from 3‐(4‐hydrazinocarbonyl‐phenyl)sydnones

The synthesis of potential fluorescent active 4‐(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)phenylhydrazine derivatives was accomplished in three steps. The key step was the dehydration cyclization of 1,2‐diacylhydrazines to form the 1,3,4‐oxadiazole ring by use of acetic anhydride/perchloric acid mixture as the dehydrating agent. The sydnone moiety served as the masked hydrazines, which could be demasked by HCl for further application. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:438–442, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20318     

Nuclear stopping power in αα anddd collisions

Inelasticαα anddd collisions were studied at a centre-of-mass energy √S _NN=31.2 GeV per nucleon-nucleon collision, using the Split-Field Magnet (SFM) detector at the CERN ISR. In this paper we show the inclusive and semi-inclusive rapidity distributions of protons, compare them with predictions of the Lund model, and calculate the average rapidity loss for participant protons. From the negative particles we calculate the inelasticity of the interaction, the average energy per particle, and the degree of isotropy of the produced hadrons.     

The excitation energy spectrum of liquid He II based on theU-matrix theory

Summary In this paper, we apply theU-matrix theory to derive an explicit expression for the excitation energy spectrum of liquid⁴He. Using a model for the effective chemical potential for⁴He, we are able to produce an excitation spectrum which is very close to the observed one. The inverse of the effective mass,i.e. 1/m ^*, is obtained as a function of momentumk. The ratio between the effective mass and the mass of helium atom atk=2.0 ?⁻¹,i.e. near the roton depth, is found to bem ^*(k=2.0 ?⁻¹)/m _He=0.18298, while the ratio atk=1.0 ?⁻¹ ism ^*(k=1.0 ?⁻¹)/m _He=−0.17103. The theoretical result of the excitation spectrum is consistent with observational data.

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Riassunto In questo lavoro si applica la teoria della matriceU per dedurre un'espressione esplicita per lo spettro d'energia di eccitazione dell'⁴He liquido. Usando un modello per il potenziale chimico efficace per l'⁴He si è in grado di produrre uno spettro di eccitazione molto simile a quello osservato. L'inverso della massa efficace, cioè 1/m ^*, è ottenuto in funzione del momentok. Si trova che il rapporto tra massa efficace e la massa dell'atomo di elio ak=2.0 ?⁻¹, cioè vicino alla profondità del rotore, èm ^* (k=2.0 ?⁻¹)/m _He= =0.18298, mentre quello ak=1.0 ?⁻¹ èm ^* (k=1.0 ?⁻¹)/m _he=−0.17103. Il risultato teorico dello spettro di eccitazione è coerente con i dati sperimentali.

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Резюме В этой статье мы применяем теориюU-матрицы для вывода явного выражения для энергетического спектра возбуждений Зидкого⁴He. Используя модель для эффективного химического потенциала для⁴He, мы воспроизводим спектр возбуждений который оказывается очень близким к зкспериментально наблюдаемому. Вычисляется обратная величина эффективной массы, т.е. 1/m ^*, как функция импульсаk. Получено отношение эффективной массы к массе атома гелия приk=2.0 ?⁻¹, которое составляетm ^* (k=2.0 ?⁻¹)/m _He=0.18298, тогда как это отношение приk=1.0 ?⁻¹ равноm ^* (k=1.0 ?⁻¹)/m _He=−0.17103. Теоретический результат для спектра возбужений согласуется с имеющимися экспериментальными данными.